1. Field of the Invention
The present invention relates generally to a silent chain including a number of link plates articulately connected by double rocker joint pins, and more particularly to a silent chain having double rocker joint pins each composed of two pins having different lengths and cross sections.
2. Description of the Related Art
Silent chains include guide links and articular links alternately arranged in the longitudinal direction of the chain and articulately connected together by pivot pins. The guide links each include a pair of laterally spaced guide plates and one or more guide link plates disposed between the guide plates. The articular links each include two or more articular link plates whose number is one more than the number of the guide link plate in each guide link. The guide plates, guide link plates and articular link plates each have a pair of pin holes at opposite ends thereof (or leading and trailing ends as viewed in the direction of movement of the silent chain). The pivot pins are inserted through the pin holes so that power can be transmitted between two adjacent links.
In one type of such silent chains, a double rocker joint pin is used as a pivot pin. The double rocker joint pin is composed of a longer pin and a shorter pin used in combination. The longer pin is located at respective leading and trailing ends of the guide plates and respective leading and trailing ends of the guide link plates, while the shorter pin is located at respective leading and trailing ends of the articular link plate.
The longer pin is fitted in two laterally aligned pin holes in the guide plates and has opposite ends projecting outwardly from the guide plates, the projecting opposite ends being swaged or riveted. The longer pin and shorter pin of each double rocker joint pin are movably received in laterally aligned pin holes of the guide and articular link plates for rocking motion relative to the link plates.
In the currently manufactured silent chains, the longer pin and the shorter pin have the same cross section, these pins of the same cross section are arranged in mirror symmetry within the same pin hole. From the viewpoint of manufacturing cost, the identical cross-sectional shape is advantageous because both pins can be manufactured by cutting off desired lengths from a single drawn wire of a certain uniform cross section. However, form the viewpoint of manufacturing process and power-transmitting operation, the longer pin and the shorter pin should preferably have different functions.
In the manufacture of the silent chain, opposite ends of the longer pins projecting outwardly from opposite outside surfaces of the guide plates are swaged or riveted. On the other hand, the shorter pin is not subjected to such swaging or riveting process. The rocker joint pin is generally elongated in shape and has a length much greater than the cross section. The longer pin has a generally semicircular cross section and hence is likely to bend when subjected to a great axial force applied during swaging of the opposite ends. Bending of the longer pin would give rise to a problem in that the overall length of the silent chain is changed and the longer pin itself may be broken during use of the silent chain.
The longer pin and shorter pin are so designed as to maintain a desired strength when they are used in combination. Accordingly, the longer pin when used alone can only provide insufficient flexural rigidity and bending strength and hence is likely to be broken. In the silent chains of the type using the rocker joint pins, only the longer pins are engaged with the guide plates. Accordingly, each longer pin is subjected to a bending force and a shear force both acting on a part of the longer pin engaged with the guide plates. Thus, during power-transmitting operation of the silent chain, the longer pin is used with more severe conditions than the shorter pin. An attempt has been made to cut down the thickness of the guide plates below the thickness of the link plates for the purpose of protecting the longer pin against undue force. However, the attempted reduction of the guide plate thickness has failed to achieve the desired purpose.
In addition, since the longer pin and the shorter pin have the same cross-sectional shape, the silent chain has a uniform pitch throughout the length thereof. This arrangement may cause a problem that secondary noise is produced due to resonance.